Thanks so much for the info. I know this may not solve the problem but i'm kinda trying to rule out the small stuff before i jump to the big stuff like replacing the oil pump. Especially since i do most of the work myself. I can't see me being able to pull the motor by myself to replace the oil pump so that means a huge repair bill i'm sure.

 

In my '02 S-10 Blazer, I used 10-30 Pennzoil. The oil pressure was 60 cold then dropped to 40 and stayed there when it warmed up. I used Mobile 1 10-30 Synthetic last oil change and now it starts out at 60 and drops to 40 then to 20-25 when idling. Goes back to 40 after accelerating to normal speed. I don't see a problem. You should keep an eye on the oil level just to be sure.

 

Thanks pewter2002. appreciate the input. i make it a habit to check the water & oil everyday before i drive it. i'm losing a little water. oil level is good. i replaced the oil pressure switch. when i pulled the old one out and examined it the plastic was broken & had separated from the metal part that screws into the block. so now it starts out about 40, drops down to 30 while driving & between 10-20 at idle. my ex was driving it back & forth from MS to OK for work & he cracked a head & the lower intake manifold, it also jumped time. i replaced those & all related gaskets, had everything reworked at a cylinder head shop, bent valves replaced, etc. new water pump, thermostat, timing chain & gears, too much to list. did all the work myself except reworking the heads. she's running pretty good now except for the little bit of lost water. i've checked all hoses, etc. nothing leaking anywhere i can see it. so i'm thinking there must be a crack in the radiator that i can't see. it seems to be leaking out overnight while it's parked. i also check it everyday when i get home & usually full then, next morning it's low so i fill it back up. replaced the radiator cap. same thing still.

 

You are welcome, but, you might want to start a new thread about the additional problems you have had and are having, specifically the coolant loss.

 

keep in mind that in high mileage engines, its normal to see a nominal loss in oil pressure that is attributed to wearing of the oil pump, bearing, piston rings, etc.

20 psi is nothing to be alarmed about. 0 psi should definitely be looked into.

mine runs 60 psi from 2000 RPM up, 1000-2000 RPM is around 40-50 psi, and at idle it drops from 40 down to 20 psi. then just for fun i switched to 10-30 oil and the pressure is a lot more stable. rock solid at 40-60 psi under all conditions. my buddy borrowed the car for a while and put 10-40 in it because "thats all they had" (yeah, right...pal) and the oil pressure was damn near 90 psi under load.

also remember that the CPI and TBI injection systems do have a lot of blowby, which can contaminate your oil very quickly. fuel in the oil dilutes the oil, which reduces pressure. when testing oil pressure make sure theres clean oil in the engine, or false readings may occur.

 

Why do the CPI and TBI have excessive blowby? I dont think the rings really care how the fuel is delivered. I would expect fuel/oil contamination being more prevelant in a carburated engine.

 

on batch fired systems, all six injectors are fired simultaneously. so potentially, you have fuel in a given cylinder for several strokes of the piston. the fuel has more time to "soak" into the film layer on the cylinder wall (as well as being pushed through the piston rings). once you turn off your engine, this film has a chance to drip back into the oil pan, contaminating the rest of the oil supply. so in essence, i guess its not blowby by definition, but the same result.

 

Fuel isn't in really in the cylinder any more than it is on a sequentially fired engine. Intake, yes. Cylinders, not really. Regardless, I wouldn't worry about it unless the engine was idling for very long periods of time where it might be a concern due to lower intake velocities, etc. During normal operation, I doubt you would see that much of a difference between a TBI, CPI, and SCFI engine on an oil analysis.

 

All right, dumb question time. What's the fuel from a CPI injected into? If it's upstream of the intake valve, I can see that it's not going to rest in the cylinder, but be sucked in with the air...but how does it remain atomized if it's injected just after the intake valve has closed?

 

It is injected into the intake runner in very much the same location as the SCFI engines. The fuel actually tends to turn to vapor in the intake runner as it sits, but at 1000RPM, the intake valve on one cylinder is opening every 0.12 seconds. There isn't a lot of time for it to sit around in there.